Understanding and applying the donor number of electrolytes in lithium metal batteries

Abstract

Donor number (DN) serves as a metric for describing the basicity of a solvent or anion and delineates the tendency to donate electrons to electron acceptors. In this review, we systematically summarize its derivation and determination methods and elucidate its impact on the performance of lithium metal batteries (LMBs). On the one hand, the DN value affects binding probability and strength with Li⁺ ions, thereby influencing the solvation environment and closely related interfacial behavior on the Li anode. On the other hand, in the case of cathodes undergoing intermediate phase change (sulfur or oxygen cathode), DN plays a pivotal role in modulating the solubility of intermediate species of sulfur (Li₂S_x, 1 < x ≤ 8) and the oxygen cathode (LiO₂). The modulation determines the equilibrium between surface-absorbed pathways and solution pathways, subsequently impacting reaction kinetics and the material utilization ratio. We believe this review would give a thorough understanding of DN and provide guidance for designing advanced electrolytes for LMBs.